Connection between a metal liner and a composite structure in the mounting region of a tank

ABSTRACT

A tank includes a tank body, a liner and a composite body spooled onto the liner, and at least one mounting, wherein the liner and the composite body are adhesively bonded together apart from in an annular joining region between the body of the tank and the mounting, surrounding the mounting.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No. PCT/EP2011/063238 International Filing date 1 Aug. 2011, which designated the United States of America, and which International Application was published under PCT Article 21 (s) as WO Publication WO 2012/016956 A1 and which claims priority to and the benefit of French Application No. 10 56418 filed on 1 Aug. 2010, the disclosures of which are incorporated by reference in their entireties.

The disclosed embodiment concerns a reservoir having a reservoir body, a liner and a composite body wrapped around the liner and at least one base plate and, in particular, the connection between a metallic liner and a composite structure in the zone of the base plate of a reservoir and is applied in particular in a high-performance reservoir of composite materials, especially a reservoir for high pressure liquid

The disclosed embodiment concerns the field of composite wound high-performance reservoirs intended for storage of liquids under pressure, especially for space applications and even more particularly for the storage of cryogenic liquids under pressure.

BACKGROUND

The term high performance reservoir refers to reservoirs optimized in terms of weight, such as are used in the transportation industry in general, space transport in particular.

The high-performance composite reservoirs intended for storage of pressurized liquids are generally designed with separation of the functions of sealing and of mechanical strength under pressure.

These reservoirs display an essentially thin shell of metal or polymer called the “liner”, whose purpose is to assure the confinement of the liquid and, in particular, the sealing and/or the protection of the wall of composite material of the reservoir with respect to the liquid

Although of optimized size, as required by the space field, one takes into account the small contribution of the liner to the mechanical strength; this shell is thin, because it does not have a structural mechanical function, and it is attempted to minimize weight.

These reservoirs also have a winding of fibers of composite material which are then deposited by filament winding on the liner. The purpose of this winding is to assure the mechanical strength of the reservoir under pressure.

The document U.S. Pat. No. 6,401,963 describes an example of a reservoir having such a liner covered with a winding of composite fibers.

One of the problems with such reservoirs is that of the behavior of the liner during the use of the reservoir and especially the successive fillings and emptyings which subject the liner alternately to compression and traction/tension.

In particular, the operations of emptying involve compression of the liner by the composite.

Now the critical stress of singeing of a liner is inversely proportional to the cube of the diameter of the reservoir in its cylindrical part

In the case when the reservoir is of small size, the liner may have a sufficient thickness to support this compression without singeing due to the technologically useful minimum and the use of the liner as a tool for winding.

In this case there is no need for precautions concerning a connection/joint between the liner and the composite.

In all other cases and especially in the case of reservoirs of large size, of a very thin liner or of very low stiffness, the liner cannot support this compression and it is then recommended to connect the liner to the composite, generally by gluing.

In the cylindrical zone of the reservoir, the relationship between the critical stress of singeing of the liner and the cube of the diameter permits a clear distinction between the case when a connection/link between the liner and the shell is not necessary and the case where it is.

A problem exists in the liner at the ends of the reservoir in the zones of the openings.

Indeed, in this zone there are relatively significant displacements between the composite shell, which is deformed under the effect of the internal pressure, and the metallic base plate which is a massive piece that deforms very little.

During the functioning of the reservoir under pressure, the total deformation of the liner connected on one side to the composite and on the other to the base plate may become very significant. The level of deformation in the liner is also accentuated by the differential thermal expansion between the metallic liner and the shell of composite. This elevated level of deformation may lead to problems of the loss of sealing during the successive cycles of operation under pressure and [varying] temperature.

In order to reduce these problems, compatibility of the deformation of the different materials among each other should be assured by a sufficient deformation of the materials.

If the liner is not glued to the composite, it is sufficient not to connect the composite to the base plates while still connecting the liner to said base plates.

The composite can then move freely, the seal and the stable positioning of the base plates being assured by the liner.

If the liner is glued to the composite, one notes at the level of the base plates a very strong increase in deformations in the liner associated with very high stresses in the glued joint between the base plate and the composite.

Classical gluing is no longer suitable, and a layer of material must be interposed, which is capable of assuring the compatibility of the deformations due to its flexibility and shearing.

This layer of a material called <<shearing fold >> is traditionally an adhesive or a elastomeric fold used for its flexibility.

The documents U.S. Pat. No. 5,287,988 and U.S. Pat. No. 3,815,773 discuss this problem and this solution.

However, there are cases where elastomeric gluing is not suitable, e.g., when a reservoir for cryogenic liquid is involved.

In fact, even today elastomeric materials do not exist which still preserve properties of sufficient flexibility at the temperatures reached by this type of reservoirs.

It is therefore necessary to find other solutions for such reservoirs.

The solution, which consists of increasing the thickness of the liner to solve the problem of singeing is not acceptable for containers of cryogenic space launchers because of their weight.

SUMMARY

The disclosed embodiment therefore has as its objective to define a link/connecting joint between the liner and composite and between liner, composite and base plate of a reservoir/container, in the case of high-pressure high-performance reservoirs optimized in terms of weight.

This link/connection has the characteristic of not being used for elastomeric gluing between the composite and the base plate of the reservoir.

The disclosed embodiment has as its particular objective the design of a cryogenic container of large dimensions using composite materials.

Within this scope, the disclosed embodiment has the goal of permitting the use of a metallic sealing liner of very low thickness and whose minimal thicknesses is defined by the requirements of the service life of the reservoir when fatigued and tolerance for damages.

To accomplish this, the disclosed embodiment proposes creation of a junction between a reservoir body displaying a liner and a composite body wound around the liner and a base plate of said reservoir through which the liner and composite body are glued to each other with the exception of an annular region surrounding the base plate.

The disclosed embodiment also involves a reservoir body, a liner and a composite body wound around the liner and at least one base plate through which the liner and composite body are glued to each other with the exception of an annular joint/junction region between the reservoir body and the base plate surrounding the base plate.

The disclosed embodiment assures the sealing in the zone of the base plate with the same strength and reliability as the existing solutions on reservoirs of more modest dimensions while assuring the storage of non-cryogenic liquid.

It also assures compatibility of the deformations between the pieces without introducing reinforcements intended to limit deformations of the capacity of the composite reservoir, permitting optimization of the dimensioning of its structure.

According to a specific mode of realization, the reservoir is of general cylindrical shape with rounded ends, at least one of said ends containing the base plate and the annular region of the junction surrounding the base plate.

The liner is preferably connected to the base plate by welding or gluing.

The base plate advantageously displays a surrounding bead or collar, said wound composite extending onto the bead without being affixed to said bead.

The composite body preferably terminates at the level of the base plate by a roll supported on the bead.

The baseplate advantageously has a central cylindrical neck, on which a loop is mounted for retaining the roll.

According to a specific mode of realization, an annular joint is arranged between the loop and the roll.

The bead is preferably of a thickness decreasing toward its periphery

According to an advantageous mode of realization, in the annular region of the joint, a layer of material of low coefficient of friction is arranged between the liner and the composite body and between the bead and the composite body.

The material with a low coefficient of friction is preferably a strip of PTFE (abbreviation for polytetrafluoroethylene).

The liner is advantageously made from pure aluminum in the annealed state.

The liner is preferably made of aluminum of the type 1050-O or 1100-O or 1050H111.

The disclosed embodiment also concerns a process for fabrication of the reservoir, in which one conducts a step of assembly of a liner with a base plate and then one winds a composite body on the liner and proceeds to a step of gluing the liner and the composite body to each other except in the annular region of the junction, between the body of the reservoir and the base plate, surrounding the base plate.

The process is advantageously such that after the step of assembling of the liner and the base plate, a material with a low coefficient of friction is applied to said annular region of the junction between the reservoir body and the base plate, surrounding the base plate, before the composite body is wound and the liner glued to the composite body.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the disclosed embodiment will become apparent from reading the following description of examples of embodiment of the disclosed embodiment with reference to the drawings, which represent:

in FIG. 1: a perspective cut-away view of the top of a reservoir according to the disclosed embodiment;

in FIG. 2: a cutaway view of a detail of FIG. 1;

on FIGS. 3A to 3D schematic cutaway views of a segment of the annular region of the joint of the reservoir in FIG. 1;

in FIG. 4: schematic cutaway views of a segment of the annular region of the junction of the reservoir in FIG. 1; and

in FIG. 5: a curve of deformation at the level of the region of the junction of the reservoir in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 represents the top of the reservoir according to the disclosed embodiment displaying a reservoir body 1, a liner 2 and a composite body 3 wound on said liner.

The reservoir is of general cylindrical shape with rounded ends, at least one of said ends displaying the base plate 4.

The baseplate 4 at the top of the reservoir serves, e.g., to hold the means of linking to the receiver to fill or empty it.

The composite body is created by winding composite fibers, such as carbon fibers impregnated by resin, and the composite body is wound on the liner and then glued (19) to the liner.

According to the disclosed embodiment, the liner 2 and the composite body 3 are glued to each other on the cylindrical part 19 and on the part of the curved surface forming the top dome of the reservoir displaying the base plate but are not glued over an annular region 5 of the joint between the reservoir body and the base plate, said annular region surrounding the base plate.

The annular region is more specifically represented in FIG. 2 viewed in a cutaway of the top of the reservoir, this annular region 5 extending toward the base plate above a bead 7 of the base plate or bead of base plate denoting the peripheral end of the base plate, the bead called the wing of the base plate in the language of the field of the disclosed embodiment and the composite wound body extending over the bead without being affixed to the bead. The annular region for which the composite body is detached from the liner and from the bead 7 of the base plate 4 is more specifically represented in FIGS. 3A to 3D depending on the conditions of use of the reservoir.

FIG. 3A represents the upper part of the reservoir displaying the annular region in cutaway view in a situation of rest, zero pressure and ambient temperature.

In this situation, the liner 2, the composite body 3 and the base plate 4 are in a position of rest without support.

Passing into the situation of FIG. 3B, for which the reservoir is brought to cryogenic temperature without pressure, e.g., at the beginning of its refilling, the liner contracts in the direction A and the composite body is pulled up against a retention loop 11 of the composite body.

When the pressure in the reservoir reaches its nominal value, as is the case in FIG. 3C, the liner is pushed toward the outside by the internal pressure Pi and, if the composite body is not glued either to the upper terminal part of the liner 2 or to the bead 7, it may move back in direction C.

Upon returning to ambient temperature (of the order of 20° C.) the liner contracts and the composite body returns to the rest position pushed into the gap between the loop 11 and bead 7 in direction D.

The absence of singeing and/or blistering of the liner during phases of returning to zero pressure and ambient temperature is assured by an optimization of the unglued length and the thickness of the liner in this zone.

Returning to FIG. 1, to facilitate the sliding of the composite body and avoid its sticking on the bead and the upper terminal part of the liner, in the annular junction region, a layer 13 of material with a low coefficient of friction or anti-adhesive is arranged between the liner and the composite body and between the bead and the composite body.

This material with a strong coefficient of friction is, for example, PTFE tape, applied around the base plate and on the terminal part of the liner by helical application of both the liner and the bead linked together by welding or gluing at the level of their junction line 6.

According to FIG. 2, in particular, the composite body terminates at the level of the base plate in a roll 9 resting on the bead 7 and held by the button 11.

The loop 11 retaining the roll is mounted on a central cylindrical neck 10 of the base plate.

An annular joint 12 is arranged between the loop and the roll in such a way that the loop presses moderately on the roll to hold it in a vertical direction parallel to the axis of symmetry of the base plate.

The neck of the base plate and the loop can be provided with complementary screw threads in order to mount the loop by screwing and thereby regulate the support of the loop on the roll. The loop can also be glued at 14 to the neck of the base plate.

The bead or the wing of the base plate 7 is of a thickness decreasing toward its periphery.

The material properties of the liner will have the following specific features:

-   -   a low elastic limit in order to limit the stresses induced in         the zone where the gluing stops,     -   a very significant ductility, especially at cryogenic         temperature in the case of a cryogenic reservoir to permit         assurance that the material will be held when static and when         fatigued under significant plastic deformation.

Pure aluminum in the annealed state (1050-O or 1100-O or 1050H111) is the preferred candidate for this liner, including in the cryogenic case.

It should be noted here that the alloys of aluminum are denoted by using a numerical system of 4 digits, which identify the chemical composition of the alloy. The series 1000 signifies at least 99% aluminum. The second digit indicates a variant of the initial alloy. Frequently this involves a smaller range of one or more elements of the alloy. The 3rd and 4th digits indicate, for the series 1000, the minimal percentage of aluminum, e.g., 1050 indicating at least 99.50% aluminum. The pieces of aluminum alloy obtained by deformation are classified in the metallurgical state. There are 5 normalized states classified by a letter. The letter “O” means “annealed”. The letter “H” which means “hammer hardened” is followed by 2 or 3 digits. The first digit indicates the type of thermomechanical range. The second digit gives the degree of hammer hardening and therefore the degree of the mechanical characteristic. The possible third digit denotes a variant.

An example of application of the disclosed embodiment is a cryogenic capacity with a diameter of 1600 mm with a liner of 1050-O aluminum with a thickness of 1 mm.

The capacity is realized by having a usage pressure of 40 bar and a breaking/rupture pressure of 80 bar.

Within this framework, the height of the capacity according to the example is represented in FIG. 4.

A blocking agent 15 closes the pin 4 and is fixed to said pin by a connection zone 16.

The loop 11 attached to the neck of the base plate 10 is supported on the roll 9 of the wound body by a material of interposition 12 intended not to harm the composite.

The wound body covers the bead of the base plate and the upper part of the liner without being glued, a possible material 13 with a low coefficient of friction being inserted between the wound body and the bead/wing assembly and the upper part of the liner.

The radius of the base plate at the level of the neck of the base plate is of the order of 196 mm, the bead extending from there from the base plate over approximately 100-120 mm and the non-glued zone extending up to a distance at the axis of revolution Z of a capacity such that the radius of the capacity reaches R500 to 510 mm at this place.

The thickness of the liner is held constant in the non-glued zone in order to minimize the peak of deformation. The variations of the possible thicknesses are localized in the zone where the liner is glued on the capacity. The liner according to this example displays a thickness e1 of 1.4 mm in the non-glued zone and e2 of 1 mm on the remainder of the reservoir, which gives a content compatible with the sought application.

The mechanical characteristics of the liner being insufficient to assure holding in the zone of the base plate, the latter is realized from a material with a high elastic limit, e.g., aluminum alloy 2219-T 87, which means that the principal alloying element is copper and that the primary phase present in the alloy is Al2Cu—Al2CuMg, T meaning that the alloy has undergone a heat treatment.

The functions of the loop 11 are, in particular, to prevent the introduction of forces to the liner and the glued joint during the non-pressurized phases, during the fabrication and/or the integration of the capacity, to keep the base plate united with the roll at the time of its cooling and to permit the displacement of the roll under the influence of internal pressure.

FIG. 6 represents the results of calculation in terms of cumulative plastic deformation of the liner along the axis Z starting at the origin and toward the zone of the base plate for the positive abscissas.

The curve 21, called MEF, represents the deformation along the liner when it is cooled.

-   -   the curve 20 called 40 b represents the deformation during         pressurization in the cold.     -   the curve 22 called the return Ob represents the deformation         during return to zero pressure, always when cold,     -   curve 23, called RT liner, represents the deformation after         returning to ambient temperature.

One notes that the maximal deformation, of the order of 8.5%, is obtained locally at the weld of liner/base plate, point 25 of FIG. 6, which corresponds to the liner/bead gluing 6 of FIG. 4, and does not exceed the properties of plasticization of the aluminum alloy 1050 chosen.

The point zero of the abscissa is a plane where the cylindrical part of the reservoir joins the bottom (where the bottom begins) and this point is called the “reference bottom.”

The negative abscissas corresponded to the cylindrical part of the reservoir, the positives to the bottom.

The point 24 of FIG. 6 is the zone where the gluing stops. It appears close to point 25, because the graphic shows axial abscissas.

In the zone of the abscissa point 0, in which the thickness of the liner changes, there are bends in the composite due to the stop of circumferential windings present in the ferrule [metal cap]. These bends result in the deformations in the liner.

In addition, in terms of the support in the glued joint of liner/bead, in traction and in shearing, the maximal values obtained are compatible with conventional adhesives.

The solution of the disclosed embodiment permits elimination of elastomeric solutions of the state of the art, which are not applicable in the case of cryogenic reservoirs.

The materials for constructing the composite wound body are, for example, from the modulated carbon fiber, intermediate type T 800 by the Toray Co. (trademark registered) or IM 7 of the Hexel Co. (trademark registered) of the numerous variants that are possible.

To connect the fibers and provide cohesion to the wound body, one will use the thermosetting resin of the epoxy type B413 M15 by Astrium or the thermoplastic resin type PA 12, a generic chemical name of a polyamide.

The joining together of the composite body and the liner is accomplished with an epoxy glue by the Hysel Co. (trademark registered) EA 9321.

Finally in the unglued zone one will use adhesive tapes of PTFE type 3M5490 by the 3M Co.

FIG. 5 corresponds to a variant of the disclosed embodiment for which the liner is created in two parts 2, 2′ glued at 17, the second part forming an annular segment connecting the first part of the liner to the bead 7 of the base plate 4.

The composite body is glued on the first part of the liner and the gluing of the composite body is extended over the second part 2′ of the liner in a zone of overlap of the two parts of the liner.

As in the example in FIG. 1, the composite body covers the second part 2′ of the liner and the bead 7 of the base plate without being glued.

This mode of realization permits creation of an excess thickness of the liner in the second part 2′ for increasing the mechanical strength of the reservoir.

For fabrication of the reservoir, one conducts a step of assembly of a liner 2 with a base plate 4 and then one winds a composite body 3 on the liner and proceeds to a step of gluing the liner 2 and the composite body 3 to each other, except in the annular region 5 of the joint between the body of the reservoir and the base plate, surrounding the base plate.

To create the annular region that is not glued, after the step of assembling of the liner and the base plate, a material with a low coefficient of friction is applied to said annular region 5 of the joint between the reservoir body and the base plate, surrounding the base plate, before the composite body is wound and the liner glued to the composite body. 

1. A reservoir comprising: a reservoir body; a metallic liner; a composite body wound around the liner; and at least one base plate, equipped with a bead, wherein at least one extremity of said at least one base plate comprises an annular junction region surrounding the bead of the base plate, and wherein the liner and the composite body are glued to each other with the exception of said annular junction region surrounding the bead of the base plate, the composite body extending over the bead without being affixed to said bead.
 2. The reservoir of claim 1, comprising a general cylindrical shape with rounded bulging ends.
 3. The reservoir of claim 1, wherein the liner is connected to the base plate by welding or gluing.
 4. The reservoir of claim 1, wherein the composite body terminates at a level of the base plate in a roll resting on the bead.
 5. The reservoir of claim 4, wherein the base plate displays a cylindrical central neck on which a loop is mounted for retaining the roll.
 6. The reservoir of claim 5, wherein an annular joint is arranged between the loop and the bead.
 7. The reservoir of claim 1, wherein the bead comprises a periphery and a thickness decreasing toward the periphery.
 8. The reservoir of claim 1, wherein in the annular junction region, a layer of material of a low coefficient of friction is arranged between the liner and the composite body and between the bead and the composite body.
 9. The reservoir of claim 8, wherein the material of low coefficient of friction is PTFE tape.
 10. The reservoir of claim 1, wherein the liner comprises annealed aluminum.
 11. The reservoir of claim 10, wherein the liner comprises type 1050-O or 1100-O or 1050H111 aluminum.
 12. The reservoir of claim 1, wherein the liner comprises a first and second part, the second part forming an annular segment connecting the first part of the liner to the bead of the base plate, the composite body being glued to the first part of the liner, the gluing of the composite body extending over the second part of the liner in a zone overlapping the first and second parts of the liner.
 13. A process for fabrication of a reservoir, comprising: assembling a liner with a base plate; winding a composite body on the liner; and gluing the liner and the composite body to each other except in an annular region of a joint between the body of the reservoir and the base plate, surrounding the base plate.
 14. The process of claim 13 comprising applying a material with a low coefficient of friction to said annular region of the joint between the reservoir body and the base plate, surrounding the base plate before the composite body is wound and the liner glued to the composite body. 